Why does AT&T lie?

I contacted AT&T via chat about my home phone service and was promised a rate reduction and added features where changes would take effect within 4 hours but the changes never happened.  Contacted them again a few days later and they were apologetic, gave me a credit and promised the changes would take effect within 48 hours. a few days later no changes.  I contacted again through chat and again they were very apologetic gave me another credit and once again promised that I changes would be made, guess what no changes 2 1/2 weeks later.  I even called but agent was a bit rude and told me that there was no way I was getting what I was promised and that I would not even have Landline service in 12-24 months.  I tried chat once more today but could only get through to sales chat, I assume because my number had been flagged on billing side.  Was told to call the number and speak to supervisor, I called got hung up on first time and the second time got and agent who was no help and so I asked for supervisor and after a couple minutes on hold I get sent to someone's voicemail.  I know I am not AT&T's biggest customer but spend almost $300 a month between home phone and 5 wireless lines but it appears as though AT&T would rather me just go away instead of honoring a price I was quoted.